The present invention relates to a full color liquid crystal driver, and, more particularly, to a full color liquid crystal driver which drives an active matrix type liquid crystal element.
FIG. 1 is an equivalent circuit diagram illustrating a full color liquid crystal display (hereinafter referred to as "LCD") of an active matrix type (see NEC, Technical Report Vol. 41 No. 5/1988). Liquid crystal pixels 21 are arranged in a matrix form, each pixels 21 connected to an amorphous silicon TFT (Thin Film Transistor) 22. Connected to those liquid crystal pixels 21 and TFTs 22 are a signal supplying circuit 23 and a scan circuit 24. In this active matrix type LCD, at the time the signal of each pixel 21 is selected, the scan circuit 24 turns the TFT 22 corresponding to that pixel 21 on to write a signal voltage in the pixel 21. During the other time, the scan circuit 24 turns that TFT 22 off to prevent the crosstalk between the adjoining pixels while holding the signal voltage in that pixel 21. In this driving system, only a signal voltage is always applied to the liquid crystal pixels, thus ensuring high-quality display.
FIG. 2 presents a block diagram illustrating a conventional full color liquid crystal driver that drives this active matrix type liquid crystal display element.
When an analog video signal in a horizontal scan period t is input from a video signal input terminal 5, an amplifier 2 amplifies this video signal to be a voltage necessary to drive a liquid crystal display (LCD) element 4 which consists of x horizontal pixels. Thus the amplifier 2 has an operation frequency of 1/(t/x). A signal output circuit 3 has a sample/hold circuit, which samples the output signal of the amplifier 2 in accordance with the individual horizontal pixels of the LCD element 4, and an output buffer, and outputs a signal at an operation frequency of 1/(t/x). This signal output circuit 3 divides the received video signal into x signals which are equal in number to the horizontal pixels of the LCD element 4 and outputs the divided signals to the LCD element 4.
According to this conventional full color liquid crystal driver, however, to provide full color display (analog display) when the number of horizontal pixels of the LCD element is increased, the frequency response of the analog amplifier 2 should be improved. In other words, the driver needs to operate at a significantly high speed, thus requiring that the amplifier 2 and the signal output circuit 3 function very fast. Due to the limited operation frequency of the amplifier 2 and the signal output circuit 3, typically used, the conventional driver has a difficulty in driving an LCD element that has a vast amount of pixels. If the amplifier 2 and signal output circuit 3 are designed to have an improved operation frequency in order to drive an LCD element having a number of horizontal pixels, their manufacturing costs become considerably high, resulting in a prominent cost increase of the driver.